Sen. Chuck Schumer came to Tribeca Sunday to endorse Daniel Squadron, his former aide who his challenging State Sen. Martin Connor in the Democratic primary this September.

Schumer and Squadron also co-wrote “Positively American: Winning Back the Middle Class Majority One Family at a Time.”

“His ability to understand and relate and come up with original and breakthrough ideas was astounding,” Schumer said at the event outside Independence Plaza North.

Squadron, 28, said “no one knows better than Sen. Schumer about winning tough senate races.” Schumer engineered the Democratic takeover of the U.S. Senate in 2006 and unseated Sen. Alfonse D’Amato in 1998.

John Scott, an I.P.N. tenant leader who is supporting Squadron, said “it’s hard to go against an incumbent. All the electeds endorse the incumbent. That’s why Schumer’s endorsement is important.”

The senate district covers much of Lower Manhattan and part of Downtown Brooklyn.

When Squadron started his campaign a few months ago, he was reluctant to criticize Connor, but he is no longer hesitant. On April 15, his campaign issued a public reminder to Connor to file his taxes, citing the tax lien Connor received a few years ago for not paying the alternative minimum tax.

Connor said the tactic was “shockingly negative in April…. I screwed up the taxes. I didn’t have the money I owed. I paid it off with interest and penalties.”

Squadron said the tax issue is about “restoring public confidence and public accountability,” but “on day one Sen. Connor started attacking me personally.”

The day Squadron announced, Connor, 62, dismissed him as a “kid.” This week Connor said “it must be nice to be young, single rich and not have to work.”

He also mentioned Squadron’s deceased father’s ties to Rupert Murdoch, the owner of Fox News and a pariah in Downtown Democratic circles. Howard Squadron, an attorney who was president of the American Jewish Congress, was also on good terms with the Clinton and Carter administrations and with former Mayor David Dinkins.

Squadron is not taking any money from political action committees and Connor, who does take PAC money, has suggested Squadron is not for the working class because he does not make exceptions for labor union PACs. Squadron has been endorsed by the Working Families Party, a pro-labor party that usually endorses Democrats.

On issues there are not many differences. Both support affordable housing, same sex marriage and congestion pricing, for example.

Squadron was well-received by a handful of voters who stopped to hear what he had to say Sunday.

Drogin smiled after Squadron answered her question on protecting affordable housing and she was impressed that Squadron had attended a recent tenants meeting at I.P.N.

“Marty better get cracking,” said Anne Compoccia, an I.P.N. resident and former neighborhood leader. Compoccia, whose known Connor for over three decades, said in recent years she has been hearing about dissatisfaction with Connor and she’s not sure why.

She said when she was a Democratic district leader in the late ‘70s, Connor’s “door was always open” when she came to him with constituents’ landlord problems. She said she asked him for similar help recently and Connor once again came through.